In the production of di(4-aminocyclohexyl)methane by the catalytic hydrogenation of di(4-aminophenyl)methane, essentially three stereoisomers are produced: ##STR1##
It is known in the art that in order to produce a corresponding isocyanate (via the known phosgenation process) which is liquid and storage stable at room temperature (i.e., from 20.degree. to 25.degree. C.), the mixture of amine stereoisomers used for phosgenation must contain the trans, trans stereoisomer in relatively narrow amounts (typically from 15 to 40% by weight).
Numerous techniques are known in the art for the production of amine mixtures containing the requisite amount of the trans, trans isomer. Typical of these known techniques are those described in U.S. Pat. Nos. 3,153,088; 3,155,724; 3,393,236; 3,644,522; 3,711,550 and 3,766,272. These known techniques generally require the separation of an amine mixture containing the requisite amount of the trans, trans isomer from an amine mixture formed after hydrogenation and containing around 50% by weight of the trans, trans isomer. Processes are known in the art for the production of a di(4-aminocyclohexyl)methane mixture containing the requisite amount of the trans, trans isomer directly from di(4-aminophenyl)methane without the need for an intermediate separation step (see, e.g., U.S. Pat. No. 2,606,928); however, the rates of reaction are much too slow for commercial application.
Numerous processes are known in the art for the production of di(4-aminocyclohexyl)methane from di(4-aminophenyl)methane via catalytic hydrogenation using supported and unsupported ruthenium catalysts. Typical of these processes are those disclosed in U.S. Pat. Nos. 2,494,563; 2,606,924; 2,606,928; 2,606,925; 3,347,917; 3,676,495; 3,959,374; 3,743,677; 3,914,307; 3,825,586; 3,636,108 and 4,161,492. While some of these processes yield an amine mixture containing the trans, trans isomer in an amount necessary to allow for the production of an isocyanate which is liquid and storage stable at room temperature, the rates of reaction are much too slow for commercial use.
Ruthenium-based catalysts have also been described as being useful in the hydrogenation of (a) polycycloaromatic polyamines formed from aniline and formaldehyde (see U.S. Pat. No. 4,226,737); (b) 2,4-bis(p-aminobenzyl)aniline (see U.S. Pat. No. 3,557,180); (c) 2,4'-diaminodiphenylmethane (see U.S. Pat. No. 3,590,002); (d) tolylene diamine/formaldehyde condensates (see U.S. Pat. Nos. 3,330,850 and 3,361,814; and (e) di(4-nitrophenyl)methane (see U.S. Pat. No. 3,742,049). However, none of these processes relate to the present problem, i.e., production of a di(4-aminocyclohexyl)methane containing from 15 to 40% by weight of the trans, trans isomer.
Finally, the use of a solvent and ammonia during the hydrogenation of di(4-aminophenyl)methane in the presence of a ruthenium catalyst is also known (see, e.g., U.S. Pat. Nos. 3,347,917; 3,636,108 and 3,644,522). The '917 patent describes the hydrogenation of di(4-aminophenyl)methane at temperatures of 180.degree. to 300.degree. C. and pressures above 500 psi in the presence of ruthenium, ammonia and solvent to obtain a high yield of di(4-aminocyclohexyl)methane rich in trans, trans isomer (i.e., above 45% by weight). The '108 patent describes the hydrogenation of di(4-aminophenyl)methane at temperatures of from 100.degree. to 300.degree. C. and pressures in excess of 200 psi in the optional presence of ammonia and solvent and in the presence of a supported ruthenium catalyst which has been alkali moderated. In those examples of the '108 patent where the trans, trans content is described as being now (Examples 21, 22 and 27), neither organic solvent nor ammonia were used. Finally, the '522 patent is similar to the '108 patent except that the ruthenium catalyst used is supported on a specific substrate. Like the '108 patent, where the trans, trans content is described as being low (Examples 17, 18 and 19), neither organic solvent nor ammonia were used.